The overall goal of the project is to define and understand the central neural circuits of pinna movement control. This system has important advantages for the study of sensorimotor systems including accessibility, availability of a good neuro-anatomical data base, and a means for quantifying movement data. Insofar as it can be considered a prototype of other motor control systems, understanding the pinna control system has relevance to humans who suffer from motor disorders. The strategy of the research employs two methodologies; 1) the application of the ablation- behavior technique in which specific neural structures or pathways are selectively interrupted and the effects both on stimulus-elicited and spontaneous pinna movements are measured; and 2) the application of neuroanatomic tract-tracing and functional labeling methods guided by the outcomes of the ablation studies to uncover additional pathways and nuclei which might contribute to pinna movements. Four specific goals are to be achieved; 1) establish the functional role of known ascending and descending components of the sound-pinna control circuit; 2) anatomically define the critical components of the system; 3) characterize the system's response to the spatial components of acoustic stimuli; and 4) develop a neural circuit model based on the results of anatomical and functional studies. In the behavioral studies, the horizontal position of the pinnae and head are electronically derived (from small coils of fine wire temporarily pasted to their posterior surfaces) both during spontaneous activity and in response to specific acoustic stimuli in awake, lightly restrained cats before and after selective ablation of selected neural sites. In the anatomic studies, conventional orthograde and retrograde tract- tracing methods are used to identify each source of inputs to the motor nuclei controlling the pinna. In addition, 2-DG labeling methods are used to identify the array of sites activated by electrical stimulation of area known or suspected to be part of the relevant circuits.